JP4118160B2 - Wafer appearance inspection system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer appearance inspection apparatus, and more particularly to an optical wafer appearance inspection apparatus suitable for inspecting defects (non-fatal defects) that do not damage the characteristics of non-inspected objects.
[0002]
[Prior art]
In the wafer process, for example, in order to form a large number of semiconductor elements on a wafer made of, for example, a silicon single crystal, a predetermined number of patterns transferred onto the wafer by an optical lithography technique are overlapped to form a multilayer structure. . In this case, the formation of individual patterns in a predetermined shape is extremely important for realizing the performance of the semiconductor element, and usually, the individual patterns are optically inspected for each layer.
[0003]
As such an inspection apparatus, for example, as described in Japanese Patent Application Laid-Open No. 2002-005849, two chips, an inspection chip and a comparison chip, out of chips regularly arranged in a lattice pattern on a wafer are disclosed. Grayscale image data is acquired by an image pickup device such as an optical microscope and a CCD camera, and a place where the grayscale difference from the same point of these two chips is larger than a preset defect determination threshold is extracted as a pattern defect. I am doing so.
[0004]
[Patent Literature]
Japanese Patent Laid-Open No. 2002-005849
[Problems to be solved by the invention]
However, in the optical wafer visual inspection apparatus as described in Japanese Patent Application Laid-Open No. 2002-005849, defects (color unevenness, grain, etc.) that do not damage the characteristics of the surface of the non-inspection object. Hereinafter, when there is a “non-fatal defect”), this non-fatal defect may be detected as a defect having a defective pattern shape. Defects detected by the optical wafer appearance inspection apparatus are often finally visually confirmed to determine whether the defect is fatal or non-fatal. Therefore, if the amount of determining non-fatal defects as defects is large, it takes time for visual confirmation.
[0006]
JP 2002-005849 A discloses that a wavelength selection filter is used, but this wavelength selection filter is preferable by switching between ultraviolet light and visible light to narrow the wavelength range of illumination light. It is used to form an optical image.
[0007]
An object of the present invention is to provide a wafer appearance inspection apparatus capable of reducing detection of non-fatal defects and shortening time required for visual confirmation.
[0008]
[Means for Solving the Problems]
(1) In order to achieve the above object, the present invention includes a light source for irradiating light on the surface of a wafer, a detector for detecting specularly reflected light from the wafer irradiated by the light source, and the wafer. The stage placed and the stage are moved, and when the difference in density detected by the detector from the same point of the inspection chip and the comparison chip on the wafer is equal to or higher than a predetermined threshold value, a control for determining a defect A plurality of wavelength selection filters having different wavelength selection ranges, and the control unit detects the brightness detected from a normal pattern portion and a non-fatal defect for the plurality of wavelength selection filters. is the measured difference in luminance, on the basis of the measurement results, among the plurality of wavelength selective filters, and brightness that is detected from the pattern normal part, from non-critical defects Difference in luminance to be issued, as compared with the case of not using the filter, select the smallest filter, is obtained so as to insert into the optical path.
With this configuration , detection of non-fatal defects can be reduced, and the time required for visual confirmation can be shortened.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of a wafer appearance inspection apparatus according to an embodiment of the present invention will be described with reference to FIGS.
First, the overall configuration of the wafer appearance inspection apparatus according to the present embodiment will be described with reference to FIG.
FIG. 1 is a block diagram showing the overall configuration of a wafer appearance inspection apparatus according to an embodiment of the present invention.
[0011]
The inspection wafer 104 is placed on the XY stage 101. On the inspection wafer 104, chips are regularly arranged in a grid pattern. The control unit 103 moves the XY stage 101 by a distance that is an integral multiple of the chip pitch.
[0012]
The inspection wafer 104 is irradiated with light from the light source 106. The light reflected from the inspection wafer 104 passes through the objective lens 105, is divided into optical paths by the half mirror 110, and is detected as a two-dimensional image by the two-dimensional CCD camera 102. As the light source 106, for example, a high-brightness xenon lamp is used.
[0013]
The control unit 103 can move the XY stage 101 by a distance that is an integral multiple of the chip pitch, and obtain a grayscale image at the same point on the inspection chip 107 and the comparison chip 108. Based on the density difference at the same point between the inspection chip 107 and the comparison chip 108, the control unit 103 determines that the point inspected by the inspection chip 107 is defective when the density difference is greater than a predetermined threshold value.
[0014]
At this time, some of the portions determined to be defects may be non-fatal defects that do not affect the performance of the semiconductor element. In order to prevent a non-fatal defect from being determined, a wavelength selection filter 109 is used in the present embodiment. The wavelength selection filter 109 is composed of four types of filters fixed to a disk and an opening portion to which no filter is attached. By rotating the disk, it is possible to insert an arbitrary type of the four types of filters into the optical path, or to insert only an opening to which no filter is attached into the optical path. The wavelength selection filter 109 is a filter that selectively transmits only light in a predetermined wavelength range. The four types of filters have different wavelength selection ranges.
[0015]
In the example illustrated in FIG. 1, the wavelength selection filter 109 is disposed between the light source 106 and the inspection wafer 104. Accordingly, only the light in the wavelength range selected by the wavelength selection filter 109 is irradiated on the inspection wafer 104. The wavelength selection filter 109 is selected so that the difference between the luminance detected from the normal pattern portion and the luminance detected from the non-fatal defect is as small as possible compared to the case where the filter 109 is not used. I try to insert it inside. How to select the wavelength selection filter 109 will be described later with reference to FIGS. For example, the wavelength selection filter 109 may be inserted in the optical path between the half mirror 110 and the CCD 102.
[0016]
Next, how to select the wavelength selection filter used in the wafer visual inspection apparatus according to the present embodiment will be described with reference to FIGS.
FIG. 2 is an example diagram showing an example of a grayscale image of an inspection wafer inspected by a wafer appearance inspection apparatus according to an embodiment of the present invention. FIG. 3 is an example diagram showing an example of a gray image of an inspection wafer to be inspected by the wafer appearance inspection apparatus according to an embodiment of the present invention and wavelength characteristics of the wavelength selection filter.
[0017]
As shown in FIG. 2, in the grayscale image of the inspection wafer inspected by the wafer appearance inspection apparatus, there are a pattern normal part 202 and a pattern background part 203. The pattern normal part 202 is a part of the metal wiring pattern formed by the metal wiring process in the wafer process. The pattern background portion 203 is a portion where no metal wiring is formed. In general, since the normal pattern portion 202 is a metal, the reflectance is high and the luminance is high. On the other hand, since the pattern background portion 203 is an insulator other than metal, the reflectance is low and the luminance is low. The non-fatal defect 201 occurs in the pattern normal part 202. That is, when the crystal grain size of the metal used for the metal wiring is increased, the reflectance of the portion is different, so that a portion having a color different from the surroundings is generated in the pattern normal portion 202. However, the non-fatal defect 201 does not affect the performance of the semiconductor element.
[0018]
In FIG. 3, a curve 202 </ b> A indicates the wavelength characteristic of the reflected light in the pattern normal part 202. This wavelength characteristic is based on the signal detected by the CCD camera 102, and includes the wavelength characteristic of the light source 106 and the wavelength characteristic of the CCD camera 102. The wavelength of the pattern normal portion 202 including the wavelength characteristic of the entire optical system. It should be called a characteristic. Since the pattern normal part 202 is a metal part, it has almost the same reflection intensity in a wide wavelength range of 400 to 600 nm, near total reflection. A curve 203A indicates the wavelength characteristic of the reflected light in the pattern background portion 203. The pattern background portion 203 has a lower reflection intensity as a whole than the pattern normal portion 202.
[0019]
A curve 201A represents the wavelength characteristic of reflected light in the non-fatal defect 201. The non-fatal defect 201 shown here has a peak wavelength at 550 nm and a light intensity in a wavelength range of 500 to 600 nm. The normal pattern portion 202 is an overall whitish image as an image detected by the CCD camera 102, whereas the non-fatal defect 201 is an image that looks green. Therefore, if it is observed with the naked eye, it can be identified that it is a non-fatal defect, but when the density difference is larger than a predetermined threshold based on the density difference at the same point between the inspection chip 107 and the comparison chip 108. In the method of determining that the point inspected by the inspection chip 107 is defective, the non-fatal defect portion is determined as a defect.
[0020]
Here, the degree of shading can be represented by the area of the wavelength characteristics shown in FIG. 3 for convenience. For example, the area in the wavelength range of 400 to 600 nm of the curve 202A of the pattern normal part 202 is S2. On the other hand, the area in the wavelength range of 400 to 600 nm of the curve 201A of the non-fatal defect 201 is S1. Since the curve 201A has a luminance distribution only in a wavelength range of 500 to 600 nm, it is substantially an area at a wavelength of 500 to 600 nm. Here, as clearly understood from the description of FIG. 3, S2 >> S1. Accordingly, in the conventional wafer appearance inspection apparatus, the difference (darkness difference) (S2−S1) between the luminance of the pattern normal portion 202 of the comparison chip 108 and the luminance of the non-fatal defect 201 at the same point is smaller than a predetermined threshold value. Therefore, the non-fatal defect 201 is determined to be a defect.
[0021]
In this embodiment, as shown in FIG. 3, the wavelength selection characteristics of the four types of filters used in the wavelength selection filter 109 of FIG. 1 are F1 (500 to 600 nm), F2 (460 to 600 nm), and F3 (440 to 600 nm). , F4 (420 to 600 nm), and when the filter is not inserted, the wavelength range is 400 to 600 nm. For example, when the filter F1 (500 to 600 nm) is inserted in the optical path, light in the wavelength range of 500 to 600 nm is irradiated to the comparison wafer and the inspection wafer. At this time, the area in the wavelength range of 500 to 600 nm of the curve 202A of the pattern normal part 202 is S2F1. On the other hand, the area in the wavelength range of 500 to 600 nm of the curve 201A of the non-fatal defect 201 is S1 as described above. Here, as understood from the description of FIG. 3, S2F1≈S1. Accordingly, the difference (darkness difference) (S2F1-S1) between the brightness of the pattern normal portion 202 of the comparison chip 108 and the brightness of the non-fatal defect 201 at the same point (S2F1-S1) is smaller than a predetermined threshold value. It can be determined that 201 is not a defect. Even if S2F1≈S1, the difference between the brightness of the pattern normal portion 202 of the comparison chip 108 and the brightness of the non-fatal defect 201 at the same point (lightness difference) (S2F1-S1) is a predetermined threshold value. If it becomes smaller than this, it can be determined that the non-fatal defect 201 is not a defect.
[0022]
By rotating the disk using the wavelength selection filter 109, four types of filters are sequentially inserted into the optical path, and the difference between the luminance detected from the normal part and the luminance detected from the non-fatal defect is Compared to a case where 109 is not used (when a simple aperture is inserted in the optical path), a non-fatal defect 201 is determined not to be a defect by selecting and using a filter that is as small as possible. It will be possible.
[0023]
As described above, in the present embodiment, a filter having a plurality of wavelength characteristics is sequentially inserted into the optical path, and the difference between the luminance detected from the normal portion and the luminance detected from the non-fatal defect is By selecting a filter that is as small as possible as compared with the case where 109 is not used and inserting it into the optical path, it is possible to determine that the non-fatal defect 201 is not a defect. By not determining a non-fatal defect as a defect, it is possible to shorten the time for identifying whether the defect is a visual defect or a non-fatal defect.
[0024]
Next, the configuration and operation of a wafer visual inspection apparatus according to another embodiment of the present invention will be described with reference to FIG. The overall configuration of the wafer visual inspection apparatus according to the present embodiment is the same as that shown in FIG.
FIG. 4 is a flowchart showing a control operation by a wafer visual inspection apparatus according to another embodiment of the present invention.
[0025]
In the present embodiment, the control unit 103 automatically performs filter selection setting.
[0026]
In step s10, the control unit 103 issues a command to the wavelength selection filter 109, inserts the nth filter into the optical path, and detects the grayscale image at that time by the CCD camera 102. In the example shown in FIG. 1, since there are four types of filters, an arbitrary nth filter is inserted into the optical path among the first to fourth filters. For example, the first filter is inserted into the optical path. Steps s10 to s30 are executed for each of the four types of filters.
[0027]
Next, in step s20, the control unit 103 moves the XY stage 101 by a distance that is an integral multiple of the chip pitch, and the nondefective defect density Def-n of the inspection chip 107 and the pattern normal part of the comparison chip 108 are detected. Obtain the concentration Pat-n.
[0028]
Next, in step s30, the control unit 103 obtains a difference Diff-n between the density Def-n of the non-fatal defect and the density Pat-n of the normal pattern part. And the above steps s10-s30 are performed about four types of filters, respectively. The resulting difference values are Diff-1, Diff-2, Diff-3, and Diff-4, respectively.
Next, in step s40, the one having the smallest difference Diff-1, Diff-2, Diff-3, or Diff-4 is selected.
[0029]
Finally, in step s50, the wavelength selection filter n having the smallest difference Diff-n is set to be inserted in the optical path.
[0030]
As described above, in this embodiment, filters having a plurality of wavelength characteristics are sequentially inserted in the optical path, and the difference between the luminance detected from the normal portion and the luminance detected from the non-fatal defect is equal to one another. By selecting the smallest filter and inserting it into the optical path, it is possible to determine that the non-fatal defect 201 is not a defect. By not determining a non-fatal defect as a defect, it is possible to shorten the time for identifying whether the defect is a visual defect or a non-fatal defect.
[0031]
【The invention's effect】
According to the present invention, detection of non-fatal defects can be reduced and the time required for visual confirmation can be shortened.
[0032]
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a wafer appearance inspection apparatus according to an embodiment of the present invention.
FIG. 2 is an example diagram showing an example of a grayscale image of an inspection wafer inspected by a wafer visual inspection apparatus according to an embodiment of the present invention.
FIG. 3 is an example diagram showing an example of a gray image of an inspection wafer to be inspected by a wafer appearance inspection apparatus according to an embodiment of the present invention and wavelength characteristics of a wavelength selection filter.
FIG. 4 is a flowchart showing a control operation by a wafer appearance inspection apparatus according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... XY stage 102 ... Two-dimensional CCD camera 103 ... Control part 104 ... Inspection wafer 105 ... Objective lens 106 ... Light source 107 ... Inspection chip 108 ... Comparison chip 109 ... Wavelength selection filter 110 ... Half mirror 201 ... Non-fatal defect 202 ... Pattern normal part 203 ... Pattern background part

Claims (1)

A light source that irradiates light on the surface of the wafer, a detector that detects specularly reflected light from the wafer irradiated by the light source, a stage on which the wafer is placed, and the stage is moved to move the wafer onto the wafer. In the wafer appearance inspection apparatus having a control unit that determines a defect when the difference in density detected by the detector from the same point of the inspection chip and the comparison chip is equal to or greater than a predetermined threshold value,
With multiple wavelength selection filters with different wavelength selection ranges,
The control unit measures a difference between luminance detected from a normal pattern portion and luminance detected from a non-fatal defect for the plurality of wavelength selection filters, and based on the measurement result,
Among these multiple wavelength selection filters, select the filter with the smallest difference between the luminance detected from the normal pattern portion and the luminance detected from the non-fatal defect compared to the case where no filter is used. A wafer appearance inspection apparatus characterized by being inserted into an optical path.

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